The initiation factor, EIf5A, is unique in that it is the only known cellular protein that contains the amino acid hypusine (Hpu) [N.sub..epsilon. -(4-amino-2-hydroxybutyl)lysine], an unusual naturally occurring amino acid, having the structure: ##STR1##
Hypusine was first isolated from bovine brain extracts by Shiba et al in 1971 [Biochim. Biophys. Acta., Vol. 244, pages 523-531 (1971)]. The molecule has two chiral centers at positions 2 and 9, each of which can be classified R or S by the Cahn-Ingold-Prelog method. The post-translational formation of the (2S, 9R) diastereomer: ##STR2##
has been shown to occur on a precursor protein of the eukaryotic initiation factor 5A, i.e., EIf5A (formerly called eIF-4D) [Cooper et al, Proc. Natl. Acad. Sci. U.S.A., Vol. 80, pages 1854-1857 (1983); and Safer, Eur. J. Biochem., Vol. 186, pages 1-3 (1989)].
EIf5A is biosynthesized by the post-translational aminobutylation of lys-51 of the precursor polypeptide followed by hydroxylation which results in hypusine at residue 51. In the mid-1970's, EIf5A was shown to stimulate ribosomal subunit joining and to enhance 80 S-bound Met-t-RNAi reactivity with puromycin [Anderson et al, FEBS Lett., Vol. 76, pages 1-10 (1977); and Kemper et al, J. Biol. Chem., Vol. 251, pages 5551-5557 (1976)]. Later in 1983, Cooper et al, supra, suggested that a hypusine-modified protein serves as an important 1-5 initiation factor in all growing eukaryotic cells. In 1986, Park et al [J. Biol. Chem., Vol. 261, pages 14515-14519 (1986)] isolated the EIf5A protein from human red blood cells and elucidated the amino acid sequence surrounding the single hypusine residue, as Thr-Gly-Hpu-His-Gly-His-Ala-Lys. EIf5A has also been found to be essential to HIV replication [Bevec et al, J. Proc. Natl. Acad. Sci. U.S.A., Vol. 91, pages 10829-10833 (1994); and Ruhl et al, J. Cell Biol., Vol. 123, pages 1309-1320 (1994)].
The initial step in the biosynthesis of EIf5A in the cell requires spermidine as the aminobutyl donor.
It is an object of the present invention to provide a method of inhibiting or preventing intracellular biosynthesis of EIf5A.